"There is no way to determine if a female is pregnant from hormone analysis and behavior alone. Mei Xiang’s hormones and behavior will mimic a pregnancy even if she is pseudopregnant, the zoo said. "The only definitive way to determine if she is pregnant is to see a developing fetus on an ultrasound."

Mei Xiang struggled to get pregnant for years after her son Tai Shan was born in 2005. She gave birth in 2012 to a cub who didn't make it. Bao Bao and a stillborn twin were born in 2013, and Bei Bei followed in 2015, along with a twin who didn't live long.